In celebration of the Captain America star's 37th birthday on Wednesday, Scott took to Instagram to share a heartwarming collage of flashback photos from their days as little kids growing up in Sudbury, Massachusetts.
"Happy birthday to my big brother! You were my first friend and you are still my best friend today," Scott wrote in the caption.
The super cute photo mosaic featured shots of the adorable brothers playing football on the beach as toddlers, wearing Goofy hats, wearing their best childhood suits and passed out in their bed as youngsters, among other pics.
"Thank you for being the greatest- I love you so damn much!!" Scott added.
Chris and Scott -- who is also an actor best known for his recurring role on One Life to Live, and a recent recurring role on Grace and Frankie -- have remained besties, and often appear together in random YouTube videos, on red carpets, and during late night talk show appearances.
Scott also made friends with Evans' on-and-off girlfriend and close pal, comedian Jenny Slate. The Hotel Artemis actress spent last Christmas with Chris's family, and posed for a photo with Scott in the family's living room.
After a deluge of sweet Happy Birthday messages from friends and family, the Avengers star took to Twitter to thank everyone for their kinds words.
"Thank you all so much for the kind birthday wishes!!!!" Chris wrote. "I’m 37 today. Or as my emotional maturity chooses to label it, the 16th anniversary of my 21st birthday."
Thank you all so much for the kind birthday wishes!!!! I’m 37 today. Or as my emotional maturity chooses to label it, the 16th anniversary of my 21st birthday.— Chris Evans (@ChrisEvans) June 13, 2018
For more adorable flashback greatness from the handsome movie star, check out this ET interview with the birthday boy from back in 2001, when ET went bowling with the soon-to-be megastar.